As anti-obesity agents or anti-diabetic agents belonging to a new category of agents without using insulin, 1-phenyl-2-[(2-phenyl-1-alkylethyl)amino] ethanol derivatives are noted since the derivatives act selectively on a .beta..sub.3 -receptor in vivo, thus having extremely low side effects. Pharmacological studies on the 1-phenyl-2-[(2-phenyl-1-alkylethyl)amino]ethanol derivatives have revealed that the .beta..sub.3.action substantially depends on (R,R)-form thereof (see J. Med.Chem., 35, 3081 (1992), and U.S. Pat. No. 5,061,727). For example, the above-mentioned U.S. Patent discloses that an (R,R)-5-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]-1,3-benzodiox ole-2,2-dicarboxylic acid disodium salt has a higher activity than the corresponding (S,S)-form by a factor of 47.
For the production of an optically active 1-phenyl-2-[(2-phenyl-1-alkylethyl)amino]ethanol derivative, there is known an optical resolution of a racemic form or a racemate, or an asymmetric synthesis.
For example, Japanese Patent Application Laid-open No. 320153/1993 (JP-A-5-320153) corresponding to the above mentioned U.S. Pat. No. 5,061,727, U.S. Pat. No. 5,106,867 and Japanese Patent Application Laid-open No. 18340/1983 (JP-A-58-18340) disclose a method of producing an (R,R)-1-phenyl-2-[(2-phenyl-1-alkylethyl)amino] ethanol derivative which comprises (1) allowing a racemic phenylethanol derivative to react with a phenylacetone derivative and a reducing agent such as sodium cyanoborohydride to produce a mixture of four species of optical isomers of a 1-phenyl-2-[(2-phenyl-1-alkylethyl)amino]ethanol derivative, (2) isolating and removing an (R,S)-isomer and an (S,R)-isomer from the mixture, and (3) optically resoluting an (R,R)-isomer and an (S,S)-isomer by a diastereomer method. According to the method, however, it is necessary to isolate and purify the only (R,R)-isomer from a mixture of the four species of optical isomers, therefore, the processes are complicated and the yield is decreased. Further, since large quantities of raw materials are required, the method is also disadvantageous in economical factors.
The above mentioned U.S. Patents and the Journal of Medicinal Chemistry disclose a method in which an (R)-3-chlorostyrene oxide derivative is allowed to react with an (R)-1-methyl-2-phenylethylamine derivative. The (R)-1-methyl-2-phenylethylamine derivative used as a raw material or reactant in the method, however, has a strong antihypnotic or arousal action and it requires particular attention when being handled, and therefore is not suited for a use in commercial production. Further, a lot of steps or processes are required to obtain the above-mentioned (R)-1-methyl-2-phenylethylamine derivative. For example, the (R)-methyl-2-phenylethylamine derivative is prepared from L-DOPA through six steps, namely, introduction of a protective group into an amino group, esterification, reduction of the resulting ester, converting a hydroxyl group to a mesyloxy group, deprotection of the protective group and reduction.
On the other hand, as a method of producing an optically active 2-amino-1-phenylethanol derivative used as a raw material or a reactant for the 1-phenyl-2-[(2-phenyl-1-alkylethyl)amino]ethanol derivative in the present invention, there is known a method of optical resolution of a corresponding racemic form with the use of an optically resoluting agent. Japanese Patent Application Laid-open No. 9979/1989 (JP-A-64-9979) (Japanese Patent Publication No. 48791/1992 (JP-B-4-48791)), for instance, discloses a method of optically resolving a racemic 2-amino-1-(3-chlorophenyl)ethanol with N-(t-butoxycarbonyl)-D-alanine to obtain an optically active (R)-form.
Further, Japanese Patent Application Laid-open No. 85247/1990 (JP-A-2-85247) discloses a method of optically resoluting a racemic 2-amino-1-(4-chlorophenyl) ethanol with using D-tartaric acid. Moreover, Journal of Japan Chemical Society, 1985, (5), pp. 910 to 913 discloses a method of optically resoluting a racemic 2-amino-1-phenylethanol with employing 3-aminobenzoic acid as a optically resolving agent.
According to these methods, however, the object optically active 2-amino-1-phenylethanol derivative can not be produced expediently and efficiently since the racemic 2-amino-1-phenylethanol derivative to be subjected to the optical resolution can not be obtained in a simple and easy manner with good yield.
For instance, as a method of producing the 2-amino-1-phenylethanol derivative, a method of reducing a nitrogen-containing compound, and a method utilizing an addition reaction of ammonia are known.
As examples of the method of reducing a nitrogen-containing compound, there are known (a) a method of reducing mandelonitrile (see J. Org. Chem., 45(14), 2785 (1980), Japanese Patent Application Laid-open No. 27/1971 (JP-A-46-27) and the like), (b) a method of reducing mandelic acid amide (refer to J. Appl. Chem., 1 (1951), 469) and (c) a method of reducing a nitro compound (see Coll. Czech. Chem. Comm., 43(7), 1917 (1978)).
In the method (a), however, since mandelonitrile is instable, the hydroxyl group is required to be protected to obtain the object compound with high yield. Further, the reaction is conducted in the presence of a great amount of a reducing agent such as LiAlH.sub.4 and NaBH.sub.4 and an activating catalyst, thus the method is disadvantageous in economical factors and requires attention to be handled. Moreover, the purity of the obtained 2-amino-1-phenylethanol derivative is low, for example, about 95%. In the methods (b) and (c), since a large quantity of LiAlH.sub.4 and the like is used as the reducing agent, there are similar problems. According to the method (c) where nitromethane is employed as a solvent it is highly dangerous and needs a sufficient care when handled.
As the method utilizing an addition reaction of ammonia, there is known (d) a method of allowing an epoxy compound to react with ammonia (see Syn. Com., 3(3), 177, (1973)), and (e) a method of allowing a halohydrin compound to react with ammonia (refer Indian. J. Chem., SECT. B, 31B, 821 (1992)). Although the reaction procedures are expedient, in these methods, however, a 1-amino-2-phenylethanol derivative as a position isomer of the 2-amino-1-phenylethanol derivative is liable to be by-produced. The position-isomer can hardly be removed by an isolating and purifying process generally used such as distillation, recrystallization and extraction, therefore, complicated procedures such as column purification are required.
On the other hand, a method of obtaining an optically active 2-amino-1-phenylethanol with the use of a microorganism is known. That is, Chemistry Express, 4, 9, 621 to 624 (1989) discloses microorganisms belonging to the genus Staphylococcus, the genus Micrococcus, the genus Rhodococcus and the genus Neisseria produce, respectively, an optically active 2-amino-1-phenylethanol from 2-amino-1-phenylethanol and .alpha.-amninoacetophenone.